You touch a length of rope that is up to 60 feet long. One end of the rope then rises into the air until the whole rope hangs perpendicular to the ground. At the upper end of the rope, an invisible entrance opens to an extradimensional space that lasts until the spell ends.
The extradimensional space can be reached by climbing to the top of the rope. The space can hold as many as eight Medium or smaller creatures. The rope can be pulled into the space, making the rope disappear from view outside the space.
Attacks and spells can't cross through the entrance into or out of the extradimensional space, but those inside can see out of it as if through a 3-foot-by-5- foot window centered on the rope.
Anything inside the extradimensional space drops out when the spell ends.
* - (powdered corn extract and a twisted loop of parchment)
its not an item so no effect
the bag says that it only has an adverse effect on being inside an item that is a dimensional space
As a DM, not a rules lawyer (so no references, just house ruling and fun with friends) :
I would personally allow the extradimensional space to move with the transport as long as:
One end of the rope is tethered via the Spell at one end(inside the Rope trick, the rope's end sits in the middle of the entrance) and the other would have to be tethered in the casting plane (to the cart, ship, lightning rail car).
IF THE ROPE WAS UNTETHERED from the CASTING PLANE - The movement the having no momentum would stop being transported (With the transport moving away with no damage, even through walls and creatures may get in the way - it's not in our space), with no one aware within the "Space" unless looking through the entrance.
IF THE ROPE WAS UNTETHERED from the extradimensional space(Rope put in a backpack), dispelled by caster, Time expires - The contents of the extradimensional space is dumped back into the Casting plane, where the entrance resides.
Known problems:
It makes the rope trick a 'balloon on a string' with a party inside: so I'd say it cannot move unless it is tethered to a structural part of the transport (towed/secured). Otherwise your ruling a free 1 hour immovable rod with the breaking strain of the rope.
My question is this:
Could you put the party members in the interdimensional space, and have a party member with Boots of Speed, grab the end of the rope and Take off running for the duration of the Boots of speed, would that Interdimensional space move with the person running with the end of the Rope.
It doesn't say anything about the Space being able to move if the Rope end is moved? I of course Say YES...