The mirrors will be pointless with a 7ft wide trailer. I tow a 6x12 and I barely see down the sides. I tow it all the time anyway and do little swerve to see around the back when I need to.
For a 7ft you might want to consider the Thor engineering and Rampage setup.
I just purchased the Z-Automotive front camera kit and plan to mount it to the back of my camper for a on dash rear view mirror.
I forgot my Thorn extensions when I took my 8' wide travel trailer home from storage (new fence & gate on sideyard went in). I drove home on surface streets on a Sunday morning, low traffic and a good thing because there was NO visibility.
The Thorn extensions are good enough for freeway travel, in my opinion. BUT, in surface street traffic, I want to see what's going on.
I am installing the wireless rear camera setup this weekend. I have a higher gain antenna and a long coax extension to run, I don't want any interference or delay.