Slide out Carpet replacement ready to install - tomorrow

[boston_blacky]

DW keeps asking why, oh why can't carpet underlay or padding go beneath the new carpet (slide-outs only) which I'll attempt to install; i.e this weekend. I recall I was advised against it - but I can not remember exactly
where I read this! If you know the answer - please advise. :@

[Old-Biscuit]

More likely due to aesthetics.

Slideout carpet will sit so much higher than the rest of carpet on main floor and the overhang portion of carpet that overlaps main floor will have a noticeable angle up to slideout

We replaced carpet in living room with opposing slideouts. Only put thin insulation material down under carpet just like OEM.