The G5RV -- more of a "bent extended double Zepp," which I think Varney would have disavowed -- I use doesn't load up well on 40 meters. It's been arranged to fit the available space and it's just not that good a match.
I don't worry much -- if you can get some energy into your antenna, it'll work even with lousy SWR -- but it was pretty bad.
So I put up an off-center-fed 40 m dipole, a sort of a coax-fed Windom.* With the feedpoint at the 80%/20% point, it should look close to 200 Ohms and take a 4:1 transformer to present a decent match to 50 Ohms.
The antenna part is easy enough -- take 67' of wire and divide accordingly, then make it fit (I ended up having to bend both ends).
The transformer... It was a holiday. The ham store we haven't got was closed. But all you really need is wire and a coil form (PVC pipe) and a little hardware: (The branch is not really that close to it.) Ended up with 11 bifilar turns of #14 house wire on approximately 1- 1/2" diameter PVC. Hams get all worked up over these but with about three bucks of materials in it, this version is not too painful to have to redo from scratch if the first try doesn't work. My design is all rule-of-thumb and fudge-factored from other versions on the Web.
Here's a funny angle on the transformer and one of the bends: It's about 20' up at the highest points.
Finished it after dark -- I'd installed a coax feedthrough but had to put the connectors on the coax -- and had a QSO within minutes of getting on the air. (Real DX: Warsaw, IN) And it tunes up on 40 meters just fine!
* Loren G. Windom, W8GZ, yet another of the antenna-designing hams from Columbus, OH. You may have heard of the other one -- W8JK, John Krause, of the 8JK HF beam and the helical antenna (both modes!).