Hi, try this:
Grab Fred's SPWW2 map editor here:
http://www.wargamer.com/Hosted/Chlan.../SP/ww2map.zip
Also grab Rocking Harrys manual on using the editor here:
http://geocities.com/rockinharry/SPWAW/FredsMapEdit.zip
Unzip Fred's editor to some directory on your hard drive. Now start it and first go to "Files" and
set SHP directory to point to your Game Data\Graphics\ (choose some shp file like actmenu.shp). Now Choose the map you want to edit from "Load Map" you need to know your map number!
Then go to:
"Options"
select: "inspection mode"
Now click on the water hex you want to change on your map.
Set Byte 0 value to 255 (this enables units to drive into the water hex "it becomes -1 shallow water hex")
Now set S29 field which should be 40 by default on water hexes to a value of 210. In value 210 infantry can wade trough the water but vehicles get stuck (imobilized). I have not experimented whit the value much, but try other values to get the vehicles to drive in the hex better. A value of 1 in data field S29 should be the same as on clear terrain and so on... Whit the inspection mode you can click on the hexes and see what values different terrain types use, etc. Repeat the actions hex by hex to make adjustments on the needed hexes always remember to press the "RETAIN" button after every chaqnge before moving to edit other hexes otherwise the values wont stick. Finaly when done editing save your map.
P.S The programs name is WW2 Map but it should work whit SPMBT also.
I am also quite novice in using the freds map editors so I dont know if Im much of help to you but perhaps some older veterans here can assist you further in using Fred Chlanda´s Map Editor better.
Screenshot: