The will get warm, but should not be extremely hot. If it is a starter solenoid, then it should not be active all the time, only when the starter is engaged. If it is a boost/charging solenoid that ties the battery banks together, then it will be active any time the ignition is on. The boost/charging solenoid needs to be of a type made specifically for continuous duty, most starter solenoids are not continuous duty.
Dan & Ro with two Rescued Boston "Terrorists"
2015 Tiffin Allegro RED 38QRA
Previously '06 Itasca Sunrise 35A on a W22 Workhorse
'12 Jeep Wrangler Sport and/or '08 Honda Goldwing