Robbbyr, that's very helpful feedback. The jacks on the Greyhawk do not fold, they come straight down, probably just like on your Seneca. For my blocks, I plan on using 1 1/2" thick pieces of wood, which I will screw and glue together so they do not slide. Based on your advise, I think I will spray them with bedliner type paint to minimize slippage. Chalking the rear wheels and setting the parking break should limit any type of movement, like you said. Based on your experience, I'm pretty optimistic about getting the unit level enough in my driveway (or street which is also sloped) enough to run my fridge.
2016 Jayco Greyhawk 29ME
2014 Jeep Wrangler Rubicon
Ready Brute Elite Tow Bar/Blue Ox Base Plate
Colorado Springs, CO