Insulating board material is not thermal mass. In order to add mass, you'd have to add something dense, like refractory, and this oven most likely doesn't have the structural strength to handle substantially more weight.
This oven was recently discussed here:http://www.pizzamaking.com/forum/index.php/topic,19857.msg194869.html#msg194869
No thermal mass in the dome and a dome height that is too high. It also puts the fire at the back, which is a lot harder to work with than the fire on the side.
It's very pretty, so hopefully you'll be able to unload the units you don't need, but, for anyone that's truly serious about making pizza, this oven most likely isn't for them.
Btw, regarding your deleted post at Forno Bravo. While I think that whenever a post is deleted, a reason should be provided (especially at a site with only a few posts a day), it really shouldn't surprise you that the post was deleted. You can't post a message about selling ovens in a forum
that sells their own ovens, regardless of whether or not you're selling them as an individual or a business.