Larry -
Lots of us (including me) use McKesh door-mount mirrors. I don't know if this is what you mean by a "strap mirror", but I love 'em. The MSRP on them is a bit frightening, but fortunately they are available from a lot of sources for a lot less.
https://hensleymfg.com/products/mckesh-mirrors/
And a couple years ago, CIPA brought out a look-alike (model 11650) to the McKesh for even less. Check Amazon or WalMart.
I agree that it is scary towing a trailer without adequate mirrors. The blind spot can kill you. I tried to diagram this out in
http://www.trailmanorowners.com/foru...ead.php?t=3658
Bill