When we bought out T2499 new in 2003, there was no caulk on the side walls, but was on the shub shower strip. See here
I found that odd they had no caulk on the side walls. So I used the best grade if white silicone I could get and caulked it up.
Then we bought the T310SR, same thing. So again I redid the same thing with the best white silicone I could get.
I found over time (~ 2-3 years) the shower basin being mounted on Styrofoam would flex, the silicone would separate from the wall and soon water could work it's way in behind the silicone.
So I tore out all the old silicone and went to a urethane type caulk another SOC member said they used. In time the same thing happened again.
After the 3rd reseal, going back to silicone, I found out the way my year camper shower basin is made. I suspect your 2006 is made the same.
Mine has about a 1" tall lip on the shower basin. It is molded all the way around except on the shower door side. Then the wall surround overlaps that 1" tall basin lip. There is about 7/8" over lap on the 3 sides, again the door side has no lip.
Now what I do is, (did this last year) I took up the shub shower rail on the door side, cleaned off all the old caulk.
Cleaned out any left over caulk on the sides to basin
Again went with the best white silicone I can get for the shub shower rail and I caulked the ends of the 2 sides that join to the door side about 1" long and stopped.
The rest of the 3 shower sides have no caulk. The over lap design of the walls to the basin is open. By caulking the 1" long ends where it ties into the shub shower screen, that keeps water from sneaking out onto the floor.
And since the walls are separate from the basin, when the shower floor flexes there is no more caulking splitting at the walls since there is no more caulk there. I let the overlap keep the water from splashing up and over.
I checked all the time last year in my shower basin inspection port of any signs of water under the shower and it's bone dry.
I now believe Sunline intended to "not" caulk the sides that have the 1" high basin lip.
We use our shower all the time. When camping, every night I shower so it gets a work out and I have not had a problem.
I got to the point I was more worried about water getting behind the caulk, festering and not being about to drain out when the caulk splits from the basin movement.
Hope this helps you sort out how you want to do yours. After 3 times re-caulking the same shower, I changed the approach. The camper is 11 years old since it was made in Nov 2003 and still dry.
PS. If you want some more pic's. I took a bunch the last time I caulked just the shower door rail, I just need to get this up on the photo server. Let me know, I'll post if it will help.