I keep my primers in a wooden US military grenade box. Separate from the powder supplies by about 20- 25 feet. (The box holds approx.30K in primers,maybe a bit more.) It would only store maybe 8-10 1# powder bottles/jugs depending on the bottle/jugs shapes.
The powders I store are in the original bottle/jugs and are simply on shelves. I currently only have 1 - 8# jug/keg left and I just have it sitting by itself on the floor.
Since I have more than 20# of smokeless powders & BP substitutes, (approx.40-50#) in 1# bottles, I just keep them in the original containers but they are separated by about 40 -50 feet from each supply or approx.20-25# each store.
I have just not gotten around to obtaining the materials & building some enclosed shelves/cabinets for them, so I just have them separated until I do find that time. Eventually I will do it, but I think that keeping them separated in my basement has been sufficient to be considered "due diligence" in making an attempt to store them reasonably well, until the cabinets are built.
I am starting to try to downsize my supplies since I am getting older & with some health issues, so I have not been shooting as much. As well, my oldest son & DIL, along with my grandsons moved to Fla., so I now don't have the extra shooters in the family to warrant larger supplies & so I may just try to use up much of the powders in the coming year to reduce the different types/quantities to a smaller number of types and save myself the need for more than one storage cabinet.
Thus, as you can see, based on the amount of powders I currently have, I would rather use wooden cabinets than a freezer or even ice chests/coolers/plastic bins for storage.
Your situation may , and likely is not the same as mine so I don't know how much of what I shared would be helpful to you.
The amount of powder you keep or intend to keep yourself (and perhaps other friends/family shooters) supplied with powders, might play into your decision(s) on their storage.
Even though not knowing the quantity of powder you have or plan to have, the below info on page 4 (of 4) of this .PDF from SAAMI might be helpful to you. I
Bolded & Underlined what I thought would be the most relative parts)
Chapter 11
Small Arms Ammunition and Primers, Smokeless Propellants,
and Black Powder Propellants
11-1 Basic Requirements.
11-1.1 In addition to all other applicable requirements of this
code, intrastate transportation of small arms ammunition, small
arms primers, smokeless propellants, and black powder shall com-
ply with US Department of Transportation Hazardous Materials
Regulations, 49 CFR, Parts 100-199.
11-1.2 This chapter applies to the channels of distribution of and
to the users of small arms ammunition, small arms primers, smoke-
less propellants, and black powder.
11-1.3 This chapter does not apply to in-process storage and
intra-plant transportation during manufacture.
11-1.4 This chapter applies to the transportation and storage of
small arms ammunition and components.
11-1.5 This chapter does not apply to safety procedures in the use
of small arms ammunition and components.
11-3 Smokeless Propellants
11-3.1 Quantities of smokeless propellants not exceeding 25 lb.
(11.3 kg) in shipping containers approved by the U.S. Department of
Transportation, may be transported in a private vehicle.
11-3.2 Quantities of smokeless propellants exceeding 25 lb.
(11.3 kg) but not exceeding 50 lb. (22.7 kg), transported in a pri-
vate vehicle, shall be transported in a portable magazine having
wood walls of at least 1 in. (25.4 mm) nominal thickness.
11-3.3 Transportation of more than 50 lb. (22.7 kg) of smokeless
propellants in a private vehicle is prohibited.
11-3.4 Commercial shipments of smokeless propellants in quanti-
ties not exceeding 100 lb. (45.4 kg) may be reclassed for trans-
portation purposes as flammable solids (Division 4.1) when pack-
aged in accordance with the U.S. Department of Transportation
Hazardous Materials Regulation (49 CFR, Part 173.171), and shall
be transported accordingly.
11-3.5 Commercial shipments of smokeless propellants exceeding
100 lb. (45.4 kg); or not packaged in accordance with the regula-
tions cited in 11-3.4 shall be transported in accordance with the
U.S. Department of Transportation regulations for Division 1.3C pro-
pellant explosives.
11-3.6 Smokeless propellants shall be stored in shipping contain-
ers approved by US Department of Transportation.
11-3.7 Smokeless propellants intended for personal use in quantities
not exceeding 20 lb. (9.1 kg) shall be permitted to be stored in original
containers in residences. Quantities exceeding 20 lb. (9.1 kg), but not
exceeding 50 lb. (22.7 kg), shall be permitted to be stored in resi-
dences where kept in a wooden box or cabinet having walls of at least
1 in. (25.4 mm) nominal thickness.
11-3.8 Not more than 20 lb. (9.1 kg) of smokeless propellants, in
containers of a 1 lb. (0.45 kg) maximum capacity shall be dis-
played in commercial establishments.
11-3.9 Commercial stocks of smokeless propellants shall be
stored as follows:
(a) Quantities exceeding 20 lb. (9.1 kg) but not exceeding 100 lb.
(45.4 kg) shall be stored in portable wooden boxes having walls of
at least 1 in. (25.4 mm) thickness.
(b) Quantities exceeding 100 lb. (45.4 kg) but not exceeding 800
lb. (363 kg) shall be stored in non-portable storage cabinets having
walls of at least 1 in. (25.4 mm) thickness. Not more than 400 lb.
(181 kg) shall be permitted to be stored in any one cabinet and
cabinets shall be separated by a distance of at least 25 ft (7.63 m)
or by a fire partition having a fire resistance of at least 1 hour. ...SNIP...
Source:
https://saami.org/wp-content/uploads/2018/01/SAAMI_ITEM_200-Smokeless_Powder.pdf
G"Luck~! whatever ya decide to do.