The easiest thing to do is probably going to be to drill a hole through the wall of the freezer (or use an existing one), and run microwave coaxial cable through the hole. Back when I worked for a wireless ISP, we used Times Microwave LMR cable for this (we were going outside the building, not into a freezer). On the freezer side, you put a low-gain outdoor-rated antenna (omni or panel, depending on location in freezer, check the radiation pattern to see that it covers the freezer), connected to the coax. Make sure to weather-seal the connection(s), you don't want water getting in.
This setup works for outdoors, your freezer will probably be a much nicer environment. No UV from the sun, etc. You can put a plastic guard over the antenna if you need to protect it from impact. Metal will block the signal.
Seal the hole in the freezer wall you run the coax through. You just want to stop air leakage. The efficiency impact on the freezer is going to be unmeasurable, as long as you don't have a lot of air leaking. (It's a ¼–⅝" hole compared to a surface area a hundred thousand times larger).
On the other side of the coax, you attach your access point. Use only one of the antenna connectors, and configure the access point to only use that antenna. (APs are usually not designed to have the two antennas on one AP in different locations, and it will cause issues).
Your coax can be basically as long as you need. Each foot of the coax causes some loss of signal strength, if you go long enough (hundreds of feet) you'll have to switch to more expensive (thicker) coax, and eventually add an amplifier inside the freezer. An outdoor amp will be fine, unless this is a -40 walk-in freezer, but keep the power low. If you need a setup with an amp (and you really shouldn't), find a wifi contractor.
Use a different access point to serve clients outside the freezer. Use the same SSID, and connect the two access points to each other with Ethernet. Each AP should be on a non-overlapping channel (use 1, 6, and 11 in the US, unless you really need more than 3, then 1, 4, 8, 11). Clients should roam between the two seamlessly.
If you have any budget for this, the folks who install satellite dishes should be able to do all of the cable & antenna work. Won't take them too long, either, so it shouldn't be that expensive. Or you could find someone who does wifi networks to handle the whole thing.