I had a brief look and I can't see anywhere that Webasto states the pump pressure. On other larger units they state 150 psi. Why not just use the normal tubing that comes with the heaters? I assume it is nylon, which is BD compatible, is very low cost and will happily do 1000 psi.
Pissing people off on the "net" since 1983.
Land Rover. Turning owners into mechanics since 1948.