the bigger the better (if it fits),i 've got an 80 watt panel which is going on my Transit roof anytime soon,if i can post a progress report with pics i will do so.Have tested this panel with a couple of 80 amp batts in pararllel and run most things in the garden shed
and batts were always topped up nicely,so the higher the wattage you can afford and if it fits on your roof is the way to go,you can never have enough charging power over here,but most importantly make sure you have a large AH capacity in your leisure battery and it is a deep cycle type not a starter/car battery,
Solarman.
added today.
Well after a break and a few more camper trips to Wales,i finally managed to fit the solar panel to the roof,it was a fiddly job
and at times it was windy up there,but it had to be done while the weather was dry!I used Tigerseal on the brackets and haven't screwed or bolted it down yet(still an option for later as i haave predrilled some screw holes in advance)Cleaned the roof where it was to be in contact with the brackets and scratched both surfaces to give a key for the sealant and put plenty on,Had to mofify the bracket with some square cutouts where the mounts are bolted for finger access behind the bolt and nuts as i wouldn't have any way of getting to them after once it was mounted.Drilled through roof for cable access and put a cable gland for weatherproofing and securing the cable against movement and finally connected it all up,Tested with a multimeter before final fixing,but now sun has gone down so will have to check charging tommorrow daytime.
Here's some pics for you....
Have been on the motorway with it today driving up to 60mph and so far it's solid,will take some pics of solar charger
showing charging readings tommorrow,
Solarman