Your right, an OBD2 reader will not work on your coach but there's a good Bluetooth alternative below.
On my 94 the OBD1 port next to the steering column about 6" above the floor.
To get any stored codes you need to bridge terminals A+B with a paper clip or similar then turn on the ignition to the Run (not start) position.
If your ECU is working fine you'll get a series of flashes from your check engine light. It works like this for example.....a code 12 would be
Code 12, one flash for 1, then a short interval then two flashes for 2 = code 12.
or a code 34 for example would be....
Code 34, three flashes for 3, short interval then four flashes for 4 =code 34.
If your ECU is working fine it will flash a code 12 three times (count the flashes) then any stored codes would flash up three times going through each stored code until you get three code 12's once again to let you know it's finished. If you get three code 12's followed by a short break then three more code 12's it's letting you know you have no stored codes.
As for an OBD1 reader I found this little gem called ALDL Droid .It works on either Android or a laptop PC. You'll need to get the software to use it with a PC .
Keep us posted.