Contrary to popular belief you do not need to build a bulky and expensive copper loop IF you make the loop 1/4 wave length long and feed the loop NEXT to the tuning capacitor. The impedance then becomes manageable, around 22 ohms, and you can use regular materials. I recommend you visit G0CWT's web site (
http://g0cwt.co.uk/magloops/ ) for loop description and follow it allowing for customization to fit your available space.
I built the 80M version using a square loop with 10ft vertical and 22ft horizontal sides, vertically mounted using camouflage tent poles as supports. I built the 3:2 matching transformer as he described and I used an 11 inch (approximate) length of RG8 coax as a tuning stub capacitor, with an extra 1/2 inch braid removed and coated with liquid tape to prevent RF arc overs. The antenna 1:1 SWR at my Saturday morning net frequency and everyone gives me excellent signal reports with my 100 watts of power. If I can hear them I can work them, very effectively.
Review the loops on Ben G0CWT's web page and use that to start with. I have since built similar smaller loops for 40 and 20M with the same amazing results, using only 14 gauge wire. Again, since the loops are 1/4 in circumference there is no need to worry about losses as you would with a compact loop.
I highly recommend using an antenna analyzer like the MFJ 259B, it makes tuning and matching much easier.
If space is very limiting you can make the 80M loop half the size but make it a two winding loop spacing the turns 4 inches apart. You will also need to add a turn or two to the primary winding on the matching transformer and trim the tuning capacitor. In this case you would have a 5ft by 11ft loop that would fit any most any small space.
BTW, these loops will outperform any mobile or coil loaded antenna since your losses are at a minimum.
Andrew