You need to determine whether the Isuzu is towable 4-down. I did a little Googling but was unable to find any info on that model year from REMCO or the FMCA Dinghy Towing Guide. It may be that the drive shaft has to be disconnected in order to tow, or it may not be towable at all. Do you have the owner's manual for the Isuzu?
As for your Vacationer...is it a diesel? (I assume so since it's a tag, but I have been wrong before.
) If it's a diesel, the weight of the Isuzu shouldn't be a problem. You will need to know the weight limits of the RV, including the hitch.