There do appear to be numerous variations on Jayco models, and even the same models of different years. I would wait for Jayco to respond, hopefully they will tell you what, if any blocking is in the slide walls. I have heard of some cases where Jayco says toppers cannot be installed because there is NO blocking.
Maybe that's why the newer 2020 models have "slide cover prep" standard. My 2020 HT was built the first week the 2020 model production of my model started, and it does NOT have the blocking or prep.
2020 Eagle HT 30.5 CKTS Modern Farmhouse (16" wheels, spring shackles set on lower hole of frame, SumoSprings TSS-107-40, standard kingpin, B&W Companion slider, TST-507 TPMS)
2019 F250 SRW SuperCab 4X4 SB 6.2 (10,000# GVW) 3.73 Axle 18" wheels