Solar advice for prewired nash camper

I want to add solar to my 2010 Nash 25r,that is "pre wired".

The controller is ment to go in an interior cabinet. The cabnet would be about 2 feet way from the roof connector and from there maybe 10-15 feet of wire to the battery. As best I can tell it is all 10g wiring. I don't want to mess with trying to fish/pull new wiring so will be using the existing wiring.

I currently have two Trojan 145 6v batteries, all led lighting and would want at least 250 watts.

So given that the wire size is less than ideal what are my options?

-with the smaller wire would a 24v panel work best?

-if I go 24v is an mppt controller the only option? Some pwm controllers work for 24 but I can't tell if they are able to step down to 12v. If so are they any good?

-would it be a really bad idea to mount the controller in the inside cabinet and then have 10+ feet of 10g wire to the battery.

-The solar wire comes into a small sealed compartment under the camper that is just a few feet from the batteries, if I mounted it here do controllers need some air flow to cool them?

Thanks for any advice