A couple of years ago a friend asked for my assistance in deciding which macerator pump to use for pretty much the same problem you have. Before spending any money, I suggested we probe the clean out drop pipe to see how far down the sewer pipe was. When it turned out the pipe was a good foot or so lower than the RV outlet about 15' away, we just dug down around the clean out and dug a trench to the RV. Then we cut the drop pipe off a couple inches above the sanitary 'T' at the house line, inserted another sanitary 'T' and ran a 4" pipe over to the RV location with an elbow, riser, and another clean out. Problem solved for about $40. If necessary, we could have cut the new 'T' into the house line to gain a few more inches of depth, but the pitch was correct without doing that.
