those panels are a great deal....I think I bought two of those from CT at 100 bucks myself....could come in handy to have a second controller too (those aren't very smart but they do the job)....BTW two 40W Coleman panels can be run through ONE of those controllers as one panel puts out max 3A and the controller is rated for 7A
good responses by Johnny about the size you need for a 13 foot trailer.....but one more factor would be WHERE it's going to be used...I notice inquirer lives in Idaho...so a power hog of a heater will probably be in his future as well as as shade.....
If it was me...for 150 bucks one could cover a lot of bases in one go....mount both on the roof...make one mount easily detachable so you can deploy one panel in bright sun if the trailer happens to be in the shade.....and then if it's high noon and sunny, if you got 80W on the roof of a 13 foot trailer you could probably sell power to your neighbours.....LOL....or to put it another way, maybe you can stay with a single
battery if you can recover used power fast enough during sunny hours
no absolutes in the
solar world....it's ALL variables.....lots of fun though...cheers all