I can find no place whatsoever to rest in the Sslal'teesh docks and/or lower caves. Thus, you can't prepare for the trip back.
The situation is made worse in that, in the first map on the way back to Sanctuary, there is a spawn point very close to the transition. Something is almost always spawned there. Since you can't rest at Sslal'teesh, you need to go to this wilderness area to rest. However, you can't rest because an "enemy is near". You either have to successfully sneak past (and likely walk a ways, since there are spawn points all over the map) or kill the encounter. Killing the encounter is unlikely, as the spawn is usually something like 6 volts, or Umber Hulk Behemoth, or some such, where you desperately need to have your protection spells ready to fight them.
It doesn't make any sense that you can't rest somewhere on the Ssal'teesh docks, given that there's a whole community there, as well as traders, and it's the safest place in the region. It seems silly that you need to go to a dangerous area in order to rest.
If there's someplace to rest at Sslal'teesh, it is either well hidden or I'm completely blind -- I checked every door, talked to every NPC, walked around every inch of the map with 14 search looking for hidden areas, and explored 3 cavernous areas below the docks, and there was nowhere I could rent a bed nor light a fire.