The gambrel garage/shop plans I am considering using for my home garage and office utilize a gambrel scissor type truss. The top cords are 2×6 and the overall the truss depth starts around 6″ and gets very deep at the top. 

I was hoping to do a more traditional build and looked at several of your cathedral and knee wall articles that discuss vented cathedral details.

It’s a 1.5 story so insulating the roof trusses will be easy as the deck will be down to walk around on.

is it worth stapling a membrane typically used for say blown in cellulose between the chords of  each truss before installing mineral wool batts to essentially make each bay between the trusses individualized . 

I would imagine it would help with wind washing but would create 1.5″ gaps above the 2×4 bottom chords. 

I was trying to avoid spray foam in any form, but considering how easy it would be for workers to work and access, should I consider it?

my concern is having the insulation essentially up at roof sheathing and then having a large cavity before sheet rock leaving a large dead space behind the gypsum board and a place for vapor to diffuse into and become trapped.

attaching a photo the the plans webpage of an example of the truss.