I have a service hatch inside the van for access to the fresh water tank, that I have noticed is a cold spot. On checking there is no insulation on it, so I am looking to put some insulation on the underside of the hatch. What is the best material to go for and best method of attachment? Would hate to use something that would then need replacing due to water ingress or mould. (Probably looking to cover an area of 60cm x 20cm). Also what is the best material for lagging external pipes? Thanks in advance.