I do use a Flight Suit/Automotive Coveralls with my CE Mark V but that is because I was going for the style of the original Game which has a more baggy look to the undersuit, as well as my armor being vacuum formed plastic. The MMKVII has a more Form Fitting appearance that the flightsuit would not fit well with. Also, the flight suit will be warm. It looks like you have already begun printing your pieces? If so, and you did not account for the thickness of a flightsuit, you will run into fitting and comfort issues.
Here is the "What's Your Undersuit?" Thread where you can get an idea of what others have used:
The 2nd entry in the hit series "What's your _____" is What's Your Undersuit? Plenty of people are asking so throw a picture of your costume, what you used and link (please be sure to embed it in text so it does not fill the page) I'll make a sample to show it off! Costume: clothing used...
www.405th.com
And here is
N8TEBB 's UnderSuit Resources Round Up, a bunch of links to how folks have made their own Undersuits:
Here is our Strapping Guide:
SO, I have had a few people asking about strapping recently. After making several suits for my husband @Kusak , I have learned a few things on what has worked for us. So, when @Lobbster contacted me to help him make his strapping I jumped on it. Our plan is to place the strapping inside his...
www.405th.com