Well, the strength of his list is speed. He doesn't have much shooting power, and he has limited combat power with the 12-man boys squads in the trukks. Does the battlewagon run with a deffrolla?
To counter his speed, I'd suggest going all jump infantry. This has the added advantage of being much more resilient in combat than a Razorspam list (not to mention you don't care as much when you get run over by a deffrolla).
12-man units of ork boys will just bounce off 10-man units of assault marines with Feel No Pain. Even a unit of 20 orks (in the battlewagon) or a unit of nobs will struggle to take them down without crippling casualties.
Here's an example:
Mephiston
Reclusiarch with jump pack
2 Sanguinary Priests with jump packs
10 Assault Marines with 2 meltaguns, 1 power fist
10 Assault Marines with 2 meltaguns, 1 power fist
10 Assault Marines with 2 meltaguns, 1 power fist
10 Assault Marines with 2 meltaguns, 1 power fist
Mephiston's a beast, and can use Wings of Sanguinius to keep up. The orks don't have any long-range shooting that he needs to worry about, so you don't really need to hide him beyond a cover save. The Priests give everyone Feel No Pain (keep your army together, don't spread out), and the Assault Marines can punch orks to death all day long without breaking a sweat. You've got plenty of scoring, the option to reserve your whole army and drop on your opponent's back line, meltaguns to basically guarantee the death of his open-topped transports, and the speed to chase him down. Give it a go, see what you think.