I have never liked having my arms inside a sleeping bag, keeping them out gets a bit cold too so I have always used a cheapish sleeping bag and a blanket over the top(it's a thick fleecy blanket and is really warm).
I would also suggest single sleeping bags with either a duvet or large blanket over the top.
A day of all things motorhome and campervan. The show is held both in the main indoor arena and across the grounds. Catering, hot drinks and food options are available. Easy access to the site and free parking included. Win one of five pairs of day tickets