There are garden hose thread adapters to 1/4 JG/polyeth tubing.
Given your usage I would just buy a RODI unit. I hate hauling liquids and clearly you do too! If you get a 25G barrel to transport to and fro, just remember that it's going to be approximately 200lbs if you round water to weigh ~8 lbs per gallon. You're most likely not going to be lifting it. Even if you can, those handles, even on a brute, might rip off! lol.
^-- Look at the specs
•Purtrex 5 Micron Sediment Filter
•MATRIKX CTO 5 Micron Carbon Block
•MATRIKX CTO 0.6 Micron Carbon Block
•75 GPD Dow Filmtec Membrane
•Single DI Refillable Cartridge
Look at Spectrapure's more basic model
Ultra-high efficiency 0.5 micron MicroTec™ Sediment Pre-Filter
0.5 micron Carbon Block Pre-Filter
The BRS unit's filters are an order of magnitude off. I can't say much about the DI beds because they're proprietary or something like that. I actually have no idea why BRS lists two specs for the carbon filters.
Any case, the point I'm trying to make is to just be aware of what you're paying for. I like higher-grade pre-sediment fliters which are cheaper to replace than resins. Whatever it doesn't catch gets passed along to the more expensive filters, so that's why I think it makes sense to get the best prefilter possible.