I do store my filaments is a 5-gallon bucket that has desiccant in it to absorb moisture. The bucket is a Gamma Lid (look at them on Amazon). I have a professional hygrometer in there and it stays around 1.5% humidity. It might be lower but hygrometers have a hard time measuring really low humility. You don't need the meter. I already had it so I put it to good use.

How I actually store each roll is like this. I purchased some 9" x 6" mesh bags and 5 lbs. of commercial desiccant It looks like translucent blue plastic BB's. It's neat and clean because it doesn't create powder or break up. When it's full of water it turns clear and that's a nice indicator. You just bake it in the oven for an hour and it's ready to go again. I put a few cups of desiccant in the mesh bag and close it off. Then I put one of those mesh bags in a 2-gallon Ziploc with the filament and squeeze out excess air. That way the desiccant is only removing moisture from a small amount of air. It's more efficient that way and keeps me from having to dryout my reusable desiccant all the time. Then, I put 3 or 4 rolls, each in their own Ziploc (along with desiccant mesh bag) into the bucket. The bottom of the bucket has one of those mesh bags too that it pulls the moisture out of the bucket air. What this does is allow me to open the bucket and remove any filament I need without adding any moist air to the other rolls because they are all individually protected. Then when I close it, the only work that has to be done is for that mesh bag in the bottom of the bucket to remove the moisture in the air again. It may be overkill but it's really simple and easy so why not? It seems to work because I've had no jams since I got my printer and no moisture issues.

I've always had this setup so I've never had moisture problems. Before I got my printer I was reading alot about them. I kept reading that the filaments absorb moisture and people were going through all kinds of repeated "oven drying" cycles to keep the filament dry. Apparently too much moisture in the filament causes gassing, pops and jams. I've never had any I think due to my initial decision to store in a dry space. Someone else will have to talk about the problems associated with moisture because I have never had to deal with it. Apparently, ABS is really a sponge. Nylon and Pet+ are not as bad from what I read.

Can you mount a rod inside the cabinet above, crack the door and have the filament spool out from in there? That actually seems kind of cool really.

I'll be on the lookout for someone else to talk knowledgeably about what a headed enclosure does to stepper motors and RAMPS. I'm just speculating as I don't have an enclosure. So, get some second opinions. But my sense is that you'll be OK. It's not going to get 300-degrees in there. I think if you had a passive (and you do already) vent in the top to let warm air escape, then that's all you need to do and it won't get too hot. You just want it warm enough to cancel out cold drafts that exacerbate warps.