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All Knuckle couplers with the exception of the Sergents couplers are compatible. Sergents work only with other Sergents couplers.
On the subject of roadbed, there's cork and foam roadbed readily available from most hobby shops. I've never used the foam myself but I hear that I works well. I didn't use and roadbed material on my current layout as it was made with all Bachmann EZ-Track.
I really like the Woodland Scenics foam roadbed. It's easy to lay and curve, sticks to both the layout and the tracks well, and is generally quieter than cork.
For all practical purposes, any brand of knuckle coupler will mate with another except the Sergents, as Jeffrey pointed out. How long one brand will hold up compared to another is a religious debate I'll avoid for right now.
There's:
cork
WS foam roadbed
Vinylbed
Homabed
EZ Bed (?) - it's that gooey stuff that you lay down with a roller
A couple companies sell wooden beveled edge roadbed
Doublesided foam mounting tape
Balsa or other softwood splines that you rip and kerf yourself
Weatherstripping
And something they use to seal camper tops (?) onto pick-up trucks - forgot the name
I'm sure you'll find others if you search this and other forums...
Yes, if you want your mainline tracks to look realistic. The whole point of a roadbed, other than something to secure the tracks to, is to simulate the raised profile of a mainline grade. Look at real railraods and you'll always see the mainline tracks are raised above the surrounding terrain. That's what the foam roadbed does for you. For yard tracks and industrial spurs, you can lay those right on the foam base of the layout, since they are generally not heavily graded and the tracks are either only a little above the terrain or, sometimes, the ties are actually sunk into the gorund.
