It's about optics - if the 'campaign bus' had SNP branding all over it, and was stored in an industrial estate in Blantyre then it looks legit. If it's a nice looking campervan and it's parked on the Chief Exec's mums drive, then it looks dodgy AF.
As ever, if you want to see what something looks like, take it out of its context and put it in another context, and see what your reaction is.
Imagine if a senior Army officer bought it from his Land Warfare Trials and Development budget, and it was parked on his mum's drive ?
Imagine if a Headteacher brought it to 'support school trips' and it was parked on his mum's drive?
Would that be 'ah, it's just muck-raking', or would that be more like 'get tae fuck pal, d'ya think I was fucking born yesterday?'...