I am a big fan of Riv-Nuts, Nut-Serts and similar. There is a nice range of sizes available in steel, stainless and aluminum. I have the insert gun McMaster Carr # 95585A800 and used it a lot when I first started using these nuts many years ago.
Sometimes in tight spaces I have to use this little tool below and love the way it works.
McMaster-Carr Part #96349A305 page 3271.
However I found that hand wrenching these nuts can take time so one day to speed up the operation I decided to try my power drivers. I have an inexpensive 3/8" pneumatic wrench and a Ryobi 1/4" hex driver impact driver. Both tools are about $40.00 each. AMAZING!!! both tools work effortlessly and with a minimum amount of practice you get perfection every time.
In tight spaces the pneumatic wrench is a godsend.
I've installed 8x32, 10x28 & 32, 1/4", 5/16", 3/8" UNF & UNC with the two power tools. You will have to hold the Nut installer tool with hand wrench which is normally required if you were hand setting it. And for added peace of mind I always hand check what I did with the power tool to make sure I did it tight enough. 95% of the time I nail it with the power tool and no further hand tightening is needed.
Take some scrap fibreglass, plastic, aluminum and steel. Drill a couple of holes and test away. I promise you will love it. Remember your holes MUST be an accurarate size for the Riv-Nut. This is half the battle. Bad size, mis-shapen hole will give poor results and frustration.
When using aluminum Riv-nuts I use antiseize on the thread otherwise you will be drilling them out when the thread galls.
Also, I use locktite locking compound on the outside of the Riv-Nut in metal.
On Fibreglass, after the Riv-Nut is installed, I use thin Super Glue Zap in the pink bottle. Capillary action sucks it into the fiberglass. I do this on both sides of the fastener wherever possible.
As for making the Rriv-Nut flush with the surface a small countersink or counterbore in the surface is all that it takes. If I cannot find the correct counterbore I make my own by grinding down a drill bit. Just make sure you grind a negative cutting edge on the tool for drilling fiberglass. And for drilling fiberglass you should always be using negative cutting edges anyway to get a clean and precise hole. Buy drill bits for plexiglass if you do not know how to grind negative bits. Regular drill bits WILL NOT make clean holes in fibreglass and can actually damage the fibreglass. McMAster Carr also sells drills for plastic/plexiglass if you need a source for making the purchase. Worth every penny and make sure you buy the exact sixe for your Riv-Nut.
Sorry to be so pedantic & verbose.
Hope this helps,
Arthur