Perfect Scale Modelbau has released a HMMWV Shelter conversion. It is item# 35124 and is available at this link:
Added to HIS 14 MAY 2014
Perfect Scale Modelbau is an aftermarket manufacturer and retailer of of conversion kits for scale military models. They are based in Germany.
They have offered several HMMWV conversions over the years.
Here are two currently available conversions.
Review of S250 Shelter on Armorama: PSM S250 Shelter Carrier Review