Underbelly Insulation

[ltoews]

I would like to add some insulation in the underbelly. The thin bubble wrap does not provide much in the way of insulation as I have had a couple of valves freeze. I tried a search wondering if someone had already posted on this subject, but no luck finding anything. It looks like the underbelly can be dropped in sections and do one section at a time. Has anyone added insulation and if so, what type and were there any special things to watch out for?

Thanks for the replies,
Larry