Adding a 3rd mobile panel

Thanks for that!! Im in a class B+ thats 25ft bumper to bumber. Just sold a 33ft 5er. Wanted something small and easy this time. Real estate on the roof is limited but looked at it today and I can fit two more panels up there so maybe 400w is the way Ill go. Bought the 40a so I could expand. I have another thing Im struggling with, Where to mount the charge controller. The only place I have inside the MH thats within a couple feet of the batteries is in a small closet. The xantrex 600w inverter is already in there. Wondering if it will get too warm in there. Other options would be 12' run of wire to the rear outside bay or a 16' run of wire to a wall towards the front of the coach. CC says max 8awg wire to the batteries. How long of a run can I get away with? Are controllers too heat sensitive to put in a 12w x 48h closet with the inverter? Thanks!!!!!!!!!!!!!!!!!!!!!