[Ram Montana High Country]

Everyone has thoughts about Nitrogen - mine is PRO Nitrogen - should be able to get it done for $20 per tire or less. Nitrogen fills generally have less moisture than compressed air / moisture in the tire is usually the biggest contributor to pressure increasing with temperatures going up. I
My place drains air, fills with nitrogen twice before set to pressure. This provides best opportunity to dry out and get highest percentage fill. Been told nitrogen molecules are larger and generally will not leak like compressed air. I’ve run tires filled both ways on the same trip - getting out and touching tires, nitrogen tires are WAY cooler.
Racers use it for this reason and more consistent pressure. Montana has many units coming out with Nitro fill ... it’s potentially cheap insurance ...
if I need top offs, I use air.

If you know someone in fire extinguishers business, they might do you cheap - they put it in fire extinguishers.

My $.02

Just look for green valve cover caps