Eeek, best not to ask the EWBS what they think of Mike Loades... I don't think any of them want anything to do with him anymore...
I wouldn't take Mike's stuff too seriously - he's great at showy stuff and getting excited, but tends to use equipment from different periods in order to prove a point that backs up his own theories.
On point, you can make up your own gambeson and try tests yourself, it's dead easy. Linen outer layer, numerous layers of cotton or wool batting and then another linen backing layer, all sewn/stapled together. See what happens!