I've been driving a van for a couple of years now, but I'm much more used to driving a car. My van is heavier and has much less power than my car and I sometimes have trouble merging onto fast roads so I'm looking for any insight from more experienced van drivers.

I don't have rear windows or a rearview mirror (only side mirrors) so visibility isn't always great. The van's also pretty slow, so I'm usually only going 50-60mph as I merge. This isn't a problem on motorways because the slip roads are so long I can plan my spot to merge easily enough. On dual carriageways where the slip roads can be really short, it feels like all I can do is put my foot down and hope. There's sometimes only a few seconds where the sliproad and main road are lined up such that I can see traffic in my mirrors, and by then I'm pretty much stuck at whatever speed my poor van has given with my foot to the floor.

Bigger and heavier vehicles than mine merge safely all the time, so I must be missing something. I'm also fairly inexperienced with such slip roads because there are no examples near me. I only encounter them a couple of times a year.