I found the best ones are Pro-Select and luckily they can be found at any Petco. They are lighter than the Midwest ones.
I did buy and have shipped to me the expen hinged wire covers from Midwest for all my expen's.
Keeps little curious CG kids from putting their hands over the expen's, heck it actually helps keep out more curious adults than children. :C
BTW: once you get the expen's your next problem will be where to store them! I bought a Square Bumper Mount RV Bike Rack on my first go around with expens.
Expen's attach to it 'perfectly'. Slip expen's thru holes of extended arms and ratchet strap them to back rails.

OR
Add hitch to the back of your MH, Toad or TT and add a cargo carrier.

4 expens' and a crate dolly on the back of my Toad! :C
