Starter Van - How big is too big?

Hello,

My family is looking for a 5 berth starter van at around £3000.

I'm struggling to find anything I like at less than 22ft but I have an aunt and uncle who are very experienced caravaners who think this is too long for a first van.

I have a Rav4 and am only looking at vans that are a suitable weight.

But should we really avoid the biggest single axles until we get used to manouvering?

What do you all think?