The aluminum siding shouldn't be an issue at that close of range. My trailer is aluminum on all four sides and the roof, yet wifi and cell signals make it in.
What's your budget? I recommend an NEMA (ip66 or ip67) enclosure, designed for outdoor installation of IT gear. If you're parked in a southern state, you want one with cooling fans. If you're in a northern state, you'll want cooling plus a heater... the heater isn't meant to keep the electronics warm, it's meant to keep condensation out. You could try skipping the heater and instead use those damp-rid packets from the dollar store, just remember to change them every now and then.
This one is pretty big, 12" x 10" ... smaller ones are a bit less expensive. Sure it's a pricey investment, but so is replacing a fried cable router every few months.
NEMA Enclosure