Back when White Dwarf showed how to make stuff from junk they came up with the Whirlwind upgrade to the Rhino Transport. All you needed were a couple of Rhino hatches, some stowage boxes, plasticard and a 40mm base. Below is a slightly modified version that I made using a couple of model robot kit bits and aluminium mesh.
You should be able to make out on the last picture the plug and socket system I made to make the Whirlwind swappable. A plastic shield and some other plastic component did the job and the Dark Angel Rhino had a round base with a corresponding socket for it to attach to.
Here's the standard version with the stowage boxes on the sides and handles as pipes
Wire mesh on the top for variety and some mounting card 'chads' hole punched out for slightly more interesting back to the Whilrwind. Lastly the Dark Angels Rhino I mentioned before with the round base with a corresponding socket for the Whirlwind to attach to.