We've got a 2-berth campervan and a small ds who will be 7mo next Easter which is realistically our first overnight away. We will be going away a lot in June/July when he'll be 9mo. He's so far quite small (25th centile).
How and where does your baby of similar age sleep? If you have some sort of bednest or travel cot what type is it? Is he up on the bed with you and dh or somewhere else? (on top of the cooker/sink?, or across the front seats??)
When our DD was small she slept in a seat box in our van. We took the lid off and put foam in the bottom for a mattress. She was fine! We went to a festival over the summer for 4 nights, a week before her first birthday, and she had grown too big for the seat box then. So we had to take the travel cot and set it up in the van. Luckily we have an awning that we put all the furniture in. There are pop up type travel cots available, which we looked at as they have a fairly small foot print. But they are pricey. Good luck and have fun!
We had our dd2 (10 months old) in bed with us. Well, in bed with me. My partner ended up sleeping in the awning with dd1 in a travel cot. She started out the night wrapped up in her pram, so we could sit inside the van (avoiding midgey's)
There would definitely be space for one of the pop up travel cots on the floor in our hired campervan, but we hadn't taken it with us.
We have a camper and one month old DS. Planning to either use the Koo-Di Pop Up Travel Bubble, which is small enough to fit at the end of our bed, or DH will sleep in the pop top and I'll cosleep with the baby. The Koo-Di is the smallest travel co I could find.