Help regarding rubber high-top bay roof seal!!

Hi

I have (and you may just about be able to see from my picture) a Palomino crazy high-top bay, and the roof is a bit of a problem.

Would anybody know where to get a cut-to-length rubber seal for this sort of thing? The gap between the roof and the van varies from being pretty tight around the sides to a few centimetres at the corners.

Also the roof really rattles if you get anywhere near 65 mph - would sealing this make any difference (ie - would the wind get inside the roof through the gaps)? Otherwise - is it a case of pulling off the interior to get to where the roof is bolted on?

Any help would be greatly appreciated - i'd like to get this monstrosity sorted out.

Plus....Does anybody else have big problems being blown around on the motorway with a high top?