Use an external one myself (polar) and it’s excellent. No condensation, complete blackout of light and keeps the van cool in sun and warmer when it’s cold outside.
Yes it’s a bit of a pain when really wet, but I carry a couple of large microfibre clothes for wiping it down, and it dries in half an hour or so with a stiff breeze or some sun.
Did look at the internal ones, but my brothers experience of condensation and mould was enough to convince me it wasn’t the better option in the round.