I need to replace my 12 volt trolling motor battery.  I have a Minkota 40 AT, 40 pound thrust motor.  My trolling battery is mounted toward the bow and does get some bounce on tough waves once in a while.  I have priced some batteries and would like your opinions, please.  Thanks. 
 
Bass Pro has a group 27 battery for $256.  It is a sealed battery.  Bass Pro is priced high but it might reflect the fact that it is a sealed unit. 
 
Batteries Plus has a group 27 for $89, but it is not sealed.   
 
Sears has a group 27 for $99, but it is not sealed.  
 
My starter battery mounted toward the stern is not sealed.  My previous trolling motor batteries were not sealed.  Should I get a battery case for a non sealed battery?  What advice can you offer on trolling batteries?