It might work for a gas motorhome but on a diesel you would want something like the VMSpc we use from http://www.silverleafelectronics.com/ or one of the ones that doesn't need a PC.   We got ours from these guys - http://www.rvupgradestore.com/SilverLeaf-VMSPC-p/vmspc.htm and run it on a small netbook.  An old notebook running Windows XP or later would also work.

I guess I like my VMSpc since it displays more info than the Scan Gauge D does without scrolling.  Here is my friend Norm's description - http://www.seeya-downtheroad.com/InformationPage/SilverleafMonitorVMSpc.html .  But if the Scan Gauge D is enough for you, it is a lot cheaper at $159.95.  In both cases you need to check which connector your diesel uses, we have a 9-pin.

We drove way out of the way twice because our diesel had a "check engine" light on to get what the codes were, so it was worth the money for us to get the VMSpc just on the price of diesel fuel.  The next time we had a check engine we knew what we were up against and could tell if we had to get it repaired "NOW" or wait.

Sorry, Windows PC only.  An old used one will work since it does not need much and the notebook does not need to be on the internet, ever, so you can set it up and not worry about updates, etc.  (Just use a USB stick to get the program and driver on).  

I put my netbook on a non-skid shelf liner piece and our dash is flat. The motorhome won't accelerate enough to cause it to hit the floor, it is not a sports car. It has a ways to go before it hits the windshield on a panic stop and so far the non-skid has done its job. Others use a Jotto Desk (one source http://jottodesk.gojotto.com/ ) or create their own setup with foam and/or sticky pads (Bed, Bath and Beyond has small ones).

I like having multiple trip meters going, seeing my real gear and the fuel tank gauge is much more accurate than the one on the dash.