Why does my video not work?
I'm not sure Chris, it works on my phone and on my pc, no issues.
How long does the drive need to be in the trailer position to cause problems with the bellows?
I think Bruce has given a good answer to this and I am reluctant to say this and would love to be specific, but there are a lot of dependants. Although all 3 bellows are designed to be pulled to the extended towing position, for towing, they are at full stretch however. The main UJ bellows has a metal spring inside it which will help keep the rubber away from the spinning UJ's when its in the down or trimmed position and this will be stretched as well, although it does spring back nicely. I've seen a few boats with their legs stored in the trailer position without an issue, but its not recommended by manufacturers for long periods.
I suppose I might be a little over dramatic and Bruce is right, if you've used manufacturers bellows and they are within the service intervals then they should be fine, but I have seen one which developed a hole in the main bellows because of this very reason when it rubbed on the UJ, let water in and it destroyed the Gimbal bearing. The UJ's were fine though and cleaned up nicely. It's sort of once bitten twice shy I suppose.
Oh by the way, nice boat and I love the way you just drive it on....very civilised.

