well, try to keep the vinyl warm till you use it – if your on-site then put the vinyl in a cardboard box in the footwell of your motor with the heaters on it and pull out each piece just prior to fitting.
If it’s an option, you could warm the van your decorating from the insode out – put a small heat source inside…this also works well with big vans and lorries using a small space heater…
You could heat gun the panel in question for a minute or so prior to decorating…
Turn the vehicle into the sun for a while prior to decorating that side…
You could arrange to get the vehicle inside (of course) 🙂
or…you could move from Scotland to somewhere warmer – like the Seychelles! 🙂
I’m sure others will have other ideas – hope this helps.
P.S. Oh! – and when you’ve finished the job go round with a hot air gun and ‘well-warm’ all the vinyl to help ‘activate’ or ‘gee-up’ the adhesive….