Henry_b
Think outside, no box required.
Watch your plugs with lpg as well they wear out the tips quickly and don’t bother with expensive plugs.My L322 runs fine on single tip Brisk plugs which were about £34 for 8. FullFat forum highly recommend them as did my service guy and also added I should try a rad cooler additive as the heads run a little hotter when using lpg.
A water "additive" will do jack shyte TBBH.
So long as the cooling system is maintained to a good degree you shouldn't have an issue.