If you are not married to an external rack, it is pretty easy to make an internal one using Blockheads,
tie down straps, and a strip of shelving. Probably costs all of $75 to DIY.
__________________
Tom DeTemple
Denver
'99 ML320 traded @139k miles for---
'02 ML320 traded @45k miles for---
'05 ML350SE now at 50k+ miles