I got one of the new Hoagie seat bags from RANS -- A lot of thought went into this seatbag design...  the ability to recline the Hoagie seat to 30 degrees or less on the Xstream can result in rubbing of the standard "Z-bag" on the tire, especially when the bag is heavily loaded.  The new Hoagie Bag has eliminated that entirely, and improved upon the storage capacity as well, with minimal weight penalty.
 
The simple aluminum support U-frame snaps quickly onto either the seatstay bolts (that extend past the locknuts) or inside the struts onto the seat strut pins themselves for secure attachment, and slips into a lower pocket on the bag, creating excellent tire clearance and solid bag support.  Overall weight of bag and support frame is just under 2 pounds -- but heck, weight weenies might even be able to take the plastic panel out of the bottom of the bag...  
 
The bag itself is well made, with 9" depth of mesh "sleeve" attachment to the seatback for a secure hold, and the mesh has a hole at the top for a headrest to stick through, if you have one.  Note that if you have your seatfoam velcro'd to the seat fabric all the way up, you'll have to remove the velcro in that top area to be able to get the bag slipped on -- it's designed to go under the foam, not over it.  There is also a clip strap underneath to secure the bag to the seat, if you plan to keep it on there all the time -- but you'll need to trim the strap length to keep the excess from hitting the tire.  Not sure if I'll use it, but it's a nice touch.
 
The five interior pockets around the sides are very nice, and the interior dimensions of the bag are roughly 16" x 10" x 8" tall, so even a large water bladder will fit inside, and tubes, etc.  There is also a reflective strip on the back, with loops for a blinkie.  
 
There might even be some aerodynamic "smoothing" contribution, like the "tailbox" concept...  and it looks good, too!  If you're getting (or have) a Xstream/F5/whatever with the Hoagie seat, this is the bag for you!  
 
This one looks like a "keeper"...  
 
Paul  
 

 

 

 

 

Looks great! Does RANS furnish longer quick-release pins for securing the bag brace legs to the seat braces?

I'm assuming you're referring to the one I already have...as the 'standard' bag.
 
I've looked into the under seat bags from Angletech in Colorado Springs (visited the store a few weeks ago when we were at my mom's) and they look to have a lot of room and would lower the COG as well.  Have you looked into anything like that?.

Quote from jayg on Jun 2^nd, 2012, 7:16pm:

 
 
The standard pins seem to be fine for this --  the outward pressure of the "spring" of the U-frame keep in in place with no problem.  The "official" instructions suggest hooking it onto the seatstay bolts at the back of the seat, in the same fashion, but the exposure of the seatpins is longer for me...
 
Jim, I think the newer standard bag works better for the SXP, but I'll have to check.  We have one...

I'll call dibs on the fastback bladder holder if it's up for sale!
 
Semper Fi