Got a very welcome early phone call from the garage that had the motorhome to let us know their mechanic had fixed the suspension bushings last night and they're completed its MOT this morning. Really excellent service (J & J McIndoe in Broxburn) and they will definitely by my first port of call for future MOT's.
We brought the motorhome back to the house and checked it over. The water pouring out the bottom when I turned the pump on initially confused me until I realised the Truma frost control valve had tripped over the winter and I needed to re-set it. Other than that it seems fine so we're going to head away for a couple of days to check it out further.
I also decided to check the MSX125 we'd just bought fitted into the garage ok and it does, with loads and loads of room to spare. Being light also made it an easy one man job to put it in there as well.
The final bit of work was to re-measure the space for the mattress to see what thickness it could take. Sadly going up to 20cm isn't going to work due to one of the windows, and even 15cm is going to need an additional cutout - so back to the companies for re-quotes and them hopefully we can get it ordered at last.