yes you can use as many panels as you want
as long as they are wired correctly and the 'controller' is large enough for the total power
120w on each side for 240w total can be done
but it means a lot of screws in the roof holding '4" brackets per panel
plus a lot of wire connections
IF you can arrange another way with larger panels, it will be less work
also there are flexible stick on panels available that might be better suited to what you want to do , than using so many small 20w panels
here are some on Amazon 68w 12v for 12v system
http://www.amazon.com/Uni-Solar-PVL-68-PowerBond-112-Inch-15-5-Inch/dp/B002MWDI44/ref=pd_sbs_lg_2peel & stick to 'CLEAN' roof
yes they work, several members have them on their rv's
i have the old style uni-solar frame mounted thin film panels
