Most 4X4 Jeeps can be towed four down without modification.
In fact, most 4X4 anythings can be towed four down IF the transfer case has a "Neutral" position.
IMO, the Owner's Manual is the final authority. When in doubt, read the instructions. If the book doesn't have any instructions about towing, the vehicle probably shouldn't be towed.
Of course, there are ALWAYS exceptions.
CM1, USN (RET)
2002 Fleetwood Southwind 32V, Ford V10
Daily Driver: '06 PT Cruiser Turbo
Toy and Toad: 2001 Dodge QC SWB, 360 Magnum, Auto, 4X4
Other toys: a pair of Kawasaki Brute Force 750 ATVs and a boat.
"When seconds count, help is only minutes away!"
Not sure about the Impala, but the Chevy Malibu can be flat towed. I'm sure that if the Impala can be flat towed, some one will chime in with that info.
Bob & Betsy(FishNFanatic) - USN Aviation Ret'd '78 & LEO Ret'd '03 & "Oath Keeper Forever" '05 HR Endeavor 40PRQ, 400 Cummins-Pulling our '11 Silverado LT, Ex Cab 6.2L NHT 4x4, w/ Rzr 800 or 570 or a Quad riding in back. Where the wheels are stopped today
I highly recomend the Chevy HHR, lots of room and fuel mileage is great and can be towed 4 down. We went with the Chevy HHR after DW done many hours of research. We tow it behind a Mobile Suites 5th wheel. Just finished a 6,000 mile trip, not issues at all. Many miles were in Colorado Rockies. Good Luck with your Choice. GBY...