I have a lovely VW lt40 that i got for my 14.2hh,now have a 15hh that i'm hoping will fit in it,if not it'll be on the market sadly. It's fab as it's great for us women who are petite,i can do the ramp easily on my own.
I can recommend the 3.5 tonne Renault Master. Nice bit of day living, horses travel backwards which is easier for them apparantly and my mare is certainly happier with that, and drives like a dream.
Try and get something with a twin axle. Prob with Renault masters is they only have a single axle. I wanted either a VWLT35 or 40, or a LDV. I ended up with an LDV, and although not the quietest or most glamourous, does the job and I enjoy driving it. Parts notoriously easy to get hold of too.