I have seen tarps chew up rigs after a while, especially when they tear and start billowing. Here in central Texas, between the UV light in the summer and buzzsaw winds in the winter, tarps do not last long. The blue tarps turn to powder in the summer, rip apart, then flay the rig alive come January to April.
The best improvised solution, if at all possible, is what ronfisherman described -- get some schedule 80 1.5" PVC pipe, some clear solvent cement (no need for the purple stuff, since this is about aesthetics, not being water tight), and go from there. The one thing I might add to that would be to have some form of fan (even if it is just a cheapie) to blow air over the top just to keep mildew from forming in a humid climate.
Of course, the absolute best solution is a carport, because if build solidly enough, one can toss solar panels on it, which can always come in handy (or maybe I am just a fan of using any south facing horizontal surface for something productive.)