Aha, you've answered a puzzle with my 3rd hand Dove whereby the last owner bought it but didn't notice excatly the same L shaped tear in the inside door vinyl just like yours. That's because it was covered by the curtains when he inspected it and didn't notice the tear until sometime later. My mate did when inspecting it for me with an interstate purchase but it was the only glitch in a good deal and being the inside flap by the door (presumably like yours pictured) I wasn't too fussed.
I had assumed perhaps the original owners might have locked themselves out and perhaps cut it trying to unlatch the door from the inside but now you mention it, they probably snagged it on the bed runner exactly like you did. In that respect it would most likely be the furthest inside door flap from the offending bed runner and normally it wouldn't be vulnerable if you only push the bed in with the canvas fully up. Lower it a bit beforehand and naturally the flap will sag inwards and be vulnerable. Elementary dear Watson after the event
Fixed mine very nicely using clear Tear Aid for VINYL (Part B) as the fabric is vinyl coated.
http://www.tear-aid.com/Just a tip here. You only get one crack at rolling it on and you don't want air bubbles so get someone to hold a flat solid object from behind (ie the cloth side) while you apply it as per instructions to the glossy side and you'll have a bubble free barely noticeable repair.
The only other way is to have the whole canvas professionally removed and a new vinyl flap sewn in and I agree you're right to be nervous about that although you're insured but there will be an excess and is it worth it? How would you feel if you went the whole hog and did it again? Perhaps explain to the Insur Co you'll let the claim go at this stage with a patch (keep a photo of the tear) and there's always the possibility of claiming in the event you really do need to remove the whole canvas for some other more serious damage. As I said the curtain hides it and it will be strong and waterproof anyway not that it needs to be with the outside flap anyway.
PS- Another reason why we all need to be very circumspect about lending out our campers to novices and why we experienced owners would never want to borrow someone elses-
http://www.myswag.org/index.php?topic=18558.0Too many things to go wrong with the simplest oversight or forgetting a strict routine for a moment.
