The joints are fine, my mate has an identical Rock Awnings Explorer to mine that we've used for the previous 2 seasons in the 750 Motor Club Locost championship.
Think I saw your and fiveoclock's cars at Silverstone earlier this year, was too busy spannering to introduce myself.
Got some spare joints just in case as they were cheap, but we never had to use them. The Surf & Turf Robusta joints are made from the same material so the difference is mainly cosmetic.
We didn't bother with extra door panels at race circuits and just rolled up an entire panel. At home I regularly drive the VX220 through the door, even though the door isn't as wide as the car I tuck the flaps behind the legs to give a 3m opening
Did loads of research when buying as I'm nerdy about these things, the Rock Awnings Explorer frame is stronger but the Surf & Turf Robusta has steel feet, can't compare the PVC fabric as one uses gsm and the other uses denier.
Being so similar I went with the one that's nearly half the price, at £239 I considered it almost a consumable but both awnings are still going strong.
I have put up these 6m x 3m on my own a few times and it's not much fun, a lot easier and only takes couple of minutes if you borrow a second person.
If you really want spend £499 get the Rhino 45, it's far far better than the Robusta and based on my experience of the Explorer it would be near indestructible but personally I don't see the point.